A conventional positioning mechanism for quickly and securely connecting an instrument to a slide assembly generally includes a keyhole slot defined in the rail of the slide assembly and a resilient member is fixed to the rail and located corresponding to the keyhole slot. The keyhole slot includes an enlarged hole and a narrow hole which communicates with the enlarged hole. The resilient member extends to the keyhole slot and covers the enlarged hole. When assembling the instrument to the slide assembly, the fixing pin on one side of the instrument is located corresponding to the keyhole slot and inserted into the enlarged hole, and then the fixing pin is shifted into the narrow hole and positioned by being biased by the resilient member, such that the instrument is connected to the rail. Generally, the rail compared with other rails of the slide assembly can be pulled out from the slide assembly and the rails are connected to the two sides of the instrument in pairs. The instrument is connected to the slide assembly on the rack so that the instrument is supported on the rack by the slide assembly.
However, when installing the instrument to the rack, the instrument is pulled out and pushed into the rack, or the vibration from the site, the fixing pin and the resilient member may have compact to each other. If the resilient member cannot bear the impact, it is easily deformed and the positioning function of the resilient member fails.
U.S. Pat. No. 7,604,307 to Greenwald et al. discloses a “telescoping slide assembly with quick-mount keyhole lock system” which provides a positioning hole for the resilient member so that when the fixing pin is inserted into the keyhole slot and shifted to a pre-set position, the fixing pin extends into the positioning hole and is well positioned.
U.S. Pat. No. 6,626,300 to Kaminski et al. discloses a “rack assembly that does not require tools for coupling chassis to slide”, wherein an end of the resilient member contacts against the fixing pin to be positioned.
Obviously, the above-mentioned disclosures provide a positioning device for positioning the instrument or chassis to the slide assembly, but the problem of the deformation of the resilient member and the potential risk to the resilient member are not resolved. Therefore, a better design for avoiding the deformation of the resilient member under impact is necessary.